For the past several years NASA's astrophysics data centers have been working together to improve and expand their services to the community, focusing particularly on providing common front-end services and on providing transparent access to each other's data holdings. Our goals are to minimize duplication of effort, build upon each other's strengths, and enable the science community to more easily utilize our complementary services. To these ends, we have established the Astrophysics Data Centers Coordinating Council. The ADEC comprises representatives from each of the NASA data centers and related information services and meets twice per year. The ADEC has been chaired by Bob Hanisch of the Space Telescope Science Institute. ADEC members also participate in the Space Science Data System Technical Working Group. The SSDS TWG works to foster interoperability and sharing of information systems technologies among all of NASA's space science enterprises.

NASA's astrophysics data centers, catalog services, and bibliographic and thematic databases are elements in a complementary and comprehensive data and information service. Included are active mission data centers (i.e., Chandra X-Ray Center and the HST Archive at STScI), wavelength-oriented archival research centers (the Infrared Science Archive, IRSA, at IPAC; the Multimission Archive at Space Telescope, MAST, at STScI; and the High Energy Astrophysics Science Archive Research Center, HEASARC, at NASA-GSFC), catalog and bibliographic information services (the Astronomical Data Center, ADC, at NASA-GSFC, and the Astrophysics Data System, ADS at SAO); and thematic/topical information data centers (the NASA Extragalactic Database, NED, at IPAC). The National Space Science Data Center (NSSDC) at NASA-GSFC provides permanent archiving for the archival research centers as well as direct access to the COBE and future SWAS and MAP mission data sets. In addition, the ADEC fosters collaboration with international data centers such as the Centre de Donnees astronomiques de Strasbourg (CDS), host to services such as SIMBAD, Vizier, and Aladdin.

An example of improved interoperability is illustrated by access to resources such as data from the EUVE and ROSAT missions. The EUVE data are physically stored at the HEASARC. EUVE data are of interest to astronomers working with X-ray data and UV data, and thus interfaces to the EUVE observation catalog have been implemented at both HEASARC and MAST. These interfaces are designed to be similar to the interfaces for other data sets at each facility, and thus there is a minimal learning curve for users of either facility to gain access to the EUVE data. MAST users can retrieve EUVE data transparently, that is, without ever being aware that the data are physically stored somewhere other than in MAST. Similarly, MAST has recently added a direct link to ROSAT data, also at HEASARC, to enable easy cross-correlation between UV/optical and X-ray data. The HST observation catalog is routinely updated and provided to ADC and CDS to enable local catalog cross-correlation, but with direct links to the HST archive for preview images and making data requests. The Digital Sky project, managed through IRSA, has constructed the first portable services for positional cross-comparison of large catalogs.

The Astrobrowse data discovery service (http://heasarc.gsfc.nasa.gov/ab/) is another example of enhanced service that has been fostered through ADEC collaborations. Astrobrowse enables researchers to make one query for data, and this query is forwarded (and reformatted as necessary) to the relevant resources known to Astrobrowse (over 1000 archive and catalog services).

A third example of interconnectivity is found in NED which returns not only basic data on individual galaxies held locally but also provides extensive sets of direct Web links for each object to catalog entries and original image databases held at NASA mission centers, and to a variety of ground-based archives around the world. NED users have transparent access to IRAS and 2MASS images via interfaces provided by IRSA.

Members of the ADEC have worked to improve links between the scientific literature and the underlying data. The ADC includes in its catalog collections many key tables from the literature, and takes on a curatorial role: reviewing tables for errors, making corrections, and then providing access via its catalog browsing and comparison tools. The ADS has pioneered efforts to interlink distributed services (electronic journals, the SIMBAD database, the ADC catalogs, and NED) and is now including links from its abstracts to archival data, enabling researchers to quickly browse--and retrieve for detailed analysis as desired--the data on which a published paper is based. ADS also links to the NED and CDS databases for many abstracts. The NED and SIMBAD name resolvers are now used throughout the community, integrated into virtually all astronomical on-line services.

The ADEC has been fostering new technological developments aimed at enabling interoperability among astronomy and space science data centers. For example, the ADC at NASA/GSFC has led community efforts in developing XML standards for astronomical catalogs, complementing efforts at IRSA, STScI, and CDS. ADEC data centers have joined in the ISAIA (Integrated System for Archival Information Access) initiative, whose goal is to define protocols and standards for queries and responses from space science data services.

The NASA astrophysics data centers will be cornerstones in the emerging National Virtual Observatory. We have already begun to establish the sort of inter-center partnerships and distributed data services that are requisite to the success of the NVO. The work of the ADEC has demonstrated the feasibility of the NVO, through support for new technology and establishment of standards. We must now take the next steps in realizing the vision of the NVO.

Robert Hanisch
Space Telescope Science Institute
Chair, Astrophysics Data Centers Coordinating Council

Bruce Berriman, George Helou
Infrared Processing and Analysis Center
Infrared Science Archive (IRSA)

Cynthia Cheung
NASA-Goddard Space Flight Center
Astronomical Data Center (ADC)

Guenther Eichhorn
Smithsonian Astrophysical Observatory
Astrophysics Data System (ADS)

Pepi Fabbiano, Arnold Rots
Smithsonian Astrophysical Observatory
Chandra X-Ray Center (CXC)

Joe King
NASA-Goddard Space Flight Center
National Space Science Data Center (NSSDC)

Barry Madore
Infrared Processing and Analysis Center
NASA Extragalactic Database (NED)

Marc Postman
Space Telescope Science Institute
Multimission Archive at Space Telescope (MAST)

Nick White
NASA-Goddard Space Flight Center
High Energy Astrophysics Science Archive Research Center (HEASARC)